1. Technical Field
The present invention relates generally to apparatus, systems and methods for reducing particle contamination for workpieces in a clean room environment or mini-environment and for transportation and storage of such workpieces. In one of its aspects, the present invention relates to a clean mini-environment for processing semiconductor wafers and transferring semiconductor wafers between locations.
2. Description of the Related Art
In an effort to reduce particulate contamination in clean environment processing of semiconductor wafers, Hewlett-Packard Company developed a standardized mechanical interface (SMIF) which is made up of enclosed portable containers known as "pods" and clean process equipment canopy as shown in U.S. Pat. Nos. 4,532,970 and 4,534,389. The wafers are placed in a pod to be carried from one process to another or to simply wait for processing. It was intended that the air or other gas surrounding the wafers inside of the pod would be stationary in order to reduce the number of particles in motion which might come into contact with one of the wafers. A pod filled with wafers is placed underneath a canopy next to a piece of equipment which performs some processing step. The canopy is closed, the pod is then opened and the wafers are removed by a mechanical arm. When the process is over, the wafers are returned to the pod. A human then opens the canopy and removes the pod. No human has touched the wafers themselves. Typically, a clean process canopy will also have a HEPA filter and an air handler so that the environment underneath the canopy is cleaner than that of the clean room.
The use of SMIF pods and hooded environments has left some problems unresolved. Their use has been an attempt to keep the semiconductor wafers as clean as possible, but they do not help remove particulates or static charge which do become associated with the wafers. This led to the development of a container which employed active filtering of the air inside the container as shown in U.S. Pat. No. 4,724,874. This departed from the original SMIF concept of trying to keep that air as still as possible. The '874 patent also shows the use of an injector/extractor for alternatively evacuating and pressurizing the interior space through a filter. It also discloses a closed recirculation system in which clean air or free N.sub.2 may be added.